In the purification treatment of organic waste waters, methods have heretofore been utilized which involve use of various microorganisms such as methane-fermenting bacteria, acid-fermenting bacteria, cellulose-decomposing bacteria and starch-decomposing bacteria. Among these methods, a method involving using phototrophic bacteria has recently aroused interest as a method which enables purification of high-concentration waste water without dilution and at the same time utilization of by-product microbial cells as resources (e.g., animal feeds, fertilizers, etc.), that is to say, a method which makes possible energy saving, resource (water) saving and utilization of discarded matter. This method is actually utilized in high-load (high-concentration) treatment of organic waste waters, for example human and domestic animal urine and feces or exrements, or effluents of the organic industry resulting from food processing, manufacture of oils and fats, sugar production, leather manufacture, etc.
This treatment method utilizing phototrophic bacteria has the defect of requiring about 7 to about 20 times as long a treating time as methods using activated sludge which are now most generally employed. Thus, in spite of its capability of high-concentration treatment of organic waste waters, its utilization in organic effluent treatment plants has not increased significantly. Some measures for shortening the treating time have been suggested heretofore (see, for example, Japanese Patent Publications Nos. 1197/67, 12631/70, 18670/71, 45881/72, 45885/72, and 43311/76).
Utilization of phototrophic bacteria in other industrial fields include a method in which a dye such as carotinoid as a microbial cell product or extract is utilized (see Japanese Patent Publication No. 9749/77 and Japanese Laid-Open Patent Publication No. 70085/77), a method of producing vitamin B.sub.12 (see Japanese Patent Publication No. 13434/70), a method of producing nucleic acid (see Japanese Laid-Open Patent Publication No. 125697/77), a method of producing antivirally active substance (see Japanese Laid-Open Patent Publication No. 155697/75), etc. Furthermore, feeds for domestic animals and fish (see Japanese Patent Publications Nos. 1353/69, 6863/70, and 16772/72), fertilizer ingredients (see Japanese Patent Publication No. 14091/70), etc. have been proposed as uses of the microbial cells themselves. Some kinds of phototrophic bacteria generate hydrogen upon absorption of solar energy, and their use as a hydrogen supply source has also been considered.
In whichever industrial field the phototrophic bacteria are utilized, promotion of the growth of the phototrophic bacteria and increasing of the quality of the microbial cells are important in increasing the utilization of the phototrophic bacteria.